1. Field of the Invention
The present invention relates to signal detection devices and clock recovery devices using the same, and in particular to a signal detection device for determining whether data is received or not when performing the digital communication in burst and a device for capturing the burst data at high speed to recover the clock which is synchronized with data symbol.
2. Description of the Background Art
Recently, the main structures of the communication equipments are mostly digitalized and a large number of multiplex systems, such as the time division system and the packet transmission system, are appearing which make good use of characteristics of the digitization.
Generally, in the reception of the burst signals (signals which are intermittently transmitted in short packets), signal detection is done by measuring levels of the receiving signals and determining that the signals are received when the levels are high. (Refer to Japanese Patent Laying-Open No.4-051618) Also, the recovery clock is made using the so-called Phase-locked Loop (referred to as PLL, hereinafter) (Refer to Japanese Patent Laying-Open No.4-119736.) That is to say, in the preamble pattern stored in the head of a data packet, a phase error between a data symbol and an oscillation output (i.e., recovered clock) of a voltage controlled oscillator is detected and fine adjustment of phase of the voltage controlled oscillator is made on the basis of the detected phase error to synchronize the oscillation output of the voltage controlled oscillator with the data symbol.
However, in such a conventional method, when receiving such signals as subjected to the time-division multiplex, it was difficult to detect data signals when the receiving signal level is near the noise level. Furthermore, when recovering clocks using the PLL, the loop time constant must be set long to prevent unstable operation in the PLL. Accordingly, long preamble pattern must be stored in the heads of data packets, which gives rise to a problem that the storage areas for the information data are short.